If you have the Stones Throw Greenhouse venue from the Sims Store it's all there for you. Unfortunately this venue gives your Sim the 'unfinished' moodlet because there is no floor to the building so your Sim can plant directly into the dirt. I add in the earth rugs from "Into the Future" expansion packs. I use whatever is the floor tile from my Sim's house and then use the rugs to cover that.
If you have none of these items or the expansion packs, you can use still grow harvestables anywhere under any roof. You will need to spend a lot of time and fertilizers to maintain and water the vegetable patch though.
This is a screenshot from my current story. As I have the aforementioned venue and expansion pack, this is how my greenhouses look. I use the 3x Window (I think that one is a base game build item called Regifted Window?) to allow more daylight into the greenhouse. The dimensions are 12x6 to allow the use of the greenhouse roof tiles.
You will notice that I use the SwiftGro Gardening Stations because they are a tremendous boon to gardeners. I use the Plants Vz Zombies
TM Sunflower (comes with the venue) which produces sunlights. Once a day, I put three sunlights into the composter and voilà, instant water, fertilize and weeding!
There is a thread on this forum about building one of these Stones Throw Greenhouses. Look for it under the Member Info and Sim Announcements/EA and Community Announcements. I hope this answers some of your questions.